bims-momema Biomed News
on Molecular mechanisms of macropinocytosis
Issue of 2022‒02‒27
five papers selected by
Harilaos Filippakis
Harvard University

  1. Biochem J. 2022 Feb 25. pii: BCJ20210855. [Epub ahead of print]
      Pancreatic ductal adenocarcinoma (PDAC) is lethal. There is a dire need for better therapeutic targets. Cancer cells have increased demand for sugars, amino acids, and lipids and therefore upregulate various nutrient transporters to meet this demand. In PDAC, SLC6A14 (an amino acid transporter) is upregulated, affecting overall patient survival. Previously we have shown using in vitro cell culture models and in vivo xenograft mouse models that pharmacological inhibition of SLC6A14 with a-methyl-L-tryptophan (a-MLT) attenuates PDAC growth. Mechanistically, blockade of SLC6A14-mediated amino acid transport with a-MLT leads to amino acid deprivation, eventually inhibiting mTORC1 signaling pathway, in tumor cells. Here we report on the effect of Slc6a14 deletion on various parameters of PDAC in KPC mice, a model for spontaneous PDAC. Pancreatic tumors in KPC mice show evidence of Slc6a14 upregulation. Deletion of Slc6a14 in this mouse attenuates PDAC growth, decreases metastatic spread of the tumor, reduces ascites fluid accumulation, and improves overall survival. At molecular level, we show lower proliferation index and reduced desmoplastic reaction following Slc6a14 deletion. Furthermore, we find that deletion of Slc6a14 does not lead to compensatory upregulation in any of the other amino transporters. In fact, some of the amino acid transporters are actually downregulated in response to Slc6a14 deletion, most likely related to altered mTORC1 signaling. Taken together, these results underscore the positive role SLC6A14 plays in PDAC growth and metastasis. Therefore, SLC6A14 is a viable drug target for treatment of PDAC and also for any other cancer that overexpresses this transporter.
    Keywords:  KPC; Pancreatic Cancer; SLC6A14; ascites fluid; metastasis; survival
  2. Biomolecules. 2022 Jan 31. pii: 235. [Epub ahead of print]12(2):
      Amino acid transporters are expressed in mammalian cells not only in the plasma membrane but also in intracellular membranes. The conventional function of these transporters is to transfer their amino acid substrates across the lipid bilayer; the direction of the transfer is dictated by the combined gradients for the amino acid substrates and the co-transported ions (Na+, H+, K+ or Cl-) across the membrane. In cases of electrogenic transporters, the membrane potential also contributes to the direction of the amino acid transfer. In addition to this expected traditional function, several unconventional functions are known for some of these amino acid transporters. This includes their role in intracellular signaling, regulation of acid-base balance, and entry of viruses into cells. Such functions expand the biological roles of these transporters beyond the logical amino acid homeostasis. In recent years, two additional unconventional biochemical/metabolic processes regulated by certain amino acid transporters have come to be recognized: macropinocytosis and obesity. This adds to the repertoire of biological processes that are controlled and regulated by amino acid transporters in health and disease. In the present review, we highlight the unusual involvement of selective amino acid transporters in macropinocytosis (SLC38A5/SLC38A3) and diet-induced obesity/metabolic syndrome (SLC6A19/SLC6A14/SLC6A6).
    Keywords:  SLC38A5/SLC38A3; SLC6A19/SLC6A14/SLC6A6; adipocyte differentiation; amino acid-dependent Na+/H+ exchange; appetite control; enteroendocrine cell; gut hormones; insulin signaling; macropinocytosis
  3. Adv Sci (Weinh). 2022 Feb 20. e2105274
      Multidrug resistance remains a great challenge for cancer chemotherapy. Herein, a biomimetic drug delivery system based on lemon-derived extracellular vesicles (EVs) nanodrugs (marked with heparin-cRGD-EVs-doxorubicin (HRED)) is demonstrated, achieving highly efficient overcoming cancer multidrug resistance. The HRED is fabricated by modifying functional heparin-cRGD (HR) onto the surface of EVs and then by loading with doxorubicin (DOX). The obtained HRED enable to effectively enter DOX-resistant cancer cells by caveolin-mediated endocytosis (main), macropinocytosis (secondary), and clathrin-mediated endocytosis (last), exhibiting excellent cellular uptake capacity. The diversified endocytosis capacity of HRED can efficiently dissipate intracellular energy and meanwhile trigger downstream production reduction of adenosine triphosphate (ATP), leading to a significant reduction of drug efflux. Consequently, they show excellent anti-proliferation capacities to DOX-resistant ovarian cancer, ensuring the efficiently overcoming ovarian cancer multidrug resistance in vivo. The authors believe this strategy provides a new strategy by endocytosis triggered-energy dissipation and ATP production reduction to design drug delivery system for overcoming cancer multidrug resistance.
    Keywords:  biomimetic nanodrugs; endocytosis; energy dissipation; lemon-derived extracellular vesicles; multidrug resistance
  4. J Anim Sci. 2022 Feb 24. pii: skac053. [Epub ahead of print]
      This study determined the oxidation of amino acids, glucose and fatty acid in enterocytes of developing chickens. Jejunal enterocytes were isolated from 0-, 7-, 21- and 42-d-old broiler chickens, and incubated at 40℃ for 30 min in Krebs-Henseleit bicarbonate buffer (pH 7.4) containing 5 mM D-glucose and one of the following: 0.5-5 mM L-[U- 14C]glutamate, 0.5-5 mM L-[U- 14C]glutamine, 0.5-5 mM L-[U- 14C]aspartate, 0.5-5 mM L-[U- 14C]alanine, 0.5-2 mM L-[U- 14C]palmitate, D-[U- 14C]glucose, 0.5-5 mM [U- 14C]propionate, and 0.5-5 mM [1- 14C]butyrate. 14CO2 produced from each 14C-labeled substrate was collected for determination of radioactivity. Among all the substrates studied, glutamate had the greatest rate of oxidation in enterocytes from 0- to 42-d-old chickens. Glutamate transaminases, rather than glutamate dehydrogenase, may be primarily responsible for initiating glutamate degradation. Rates of amino acid and fatty acid oxidation by cells increased (P ˂ 0.05) with increasing their extracellular concentrations from 0.5 to 5 mM. Rates of glutamate and glucose oxidation in enterocytes decreased (P ˂ 0.05) with increasing age, and rates of glutamine, aspartate, propionate and butyrate oxidation were lower (P ˂ 0.05) in 42-d-old chickens than in 0-d-old chickens. By contrast, oxidation of palmitate at 2 mM increased (P ˂ 0.05) by 118% in cells from 42-d-old chickens, compared with 0-d-old chickens. Compared with glutamate, oxidation of glutamine, aspartate, alanine, propionate, butyrate and palmitate was limited in cells from all age groups of chickens. Collectively, these results indicate that glutamate is the major metabolic fuel in enterocytes of 0- to 42-d-old chickens.
    Keywords:  amino acids; chickens; energy substrates; enterocytes; glucose; intestine
  5. Breast. 2022 Feb 20. pii: S0960-9776(22)00036-4. [Epub ahead of print]62 152-161
      AIMS: The study aimed to search novel, simple and practical index reflecting the level of essential amino acids (EAAs) metabolism in breast cancer (BC), as well as to explore the effect of enhanced EAAs metabolism on the prognosis and immune microenvironment of BC, thus providing new evidence for the application of EAAs deprivation in the BC treatment.METHODS: The study includes the analysis of multi-omics and clinical data of 13 BC cell lines and 2898 BC patients in the public database. Further validation was performed using multi-omics and immunohistochemistry data from 83 BC tissue samples collected at our hospital.
    RESULTS: According to the multi-omics data, the SLC7A5 to SLC7A8 Ratio (SSR) score was found to be significantly correlated with the EAAs level and EAAs-metabolic activity of BC, suggesting that the SSR score might be used as a biomarker to assess the degree of EAAs metabolism in BC. Besides, BC patients with high EAAs metabolism had shorter overall survival (OS) time, higher PD-L1 expression, and higher T regulatory cells (Tregs) infiltration, indicating that a high EAAs metabolism was related to a poor prognosis and immune suppression in BC. Additionally, MYC amplification is a critical molecular process in the metabolic reprogramming of EAAs in BC.
    CONCLUSION: EAAs may be a possible therapeutic target for BC treatment.
    Keywords:  Breast cancer; Essential amino acid; Metabolic reprogramming; PD-L1; Tregs